You’ll need to let us know a little more, please. Where are you running in to difficulties? What and where is the error you’re receiving? Is the Beam / one SLs / Subs WiFi turned on? You do have two One SLs for use as surrounds? How is your system connected to your LAN? If by WiFi, which band are you using?

Reading this a different way, are you trying to connect the Sonos Sub to two different Sonos ‘rooms’? If so, you can’t do that. You could move the Sub between Sonos ‘rooms’, by removing it from one, and adding it to the other when desired. You’d lose any TruePlay each time if you’re using that. And while it can be done, it takes time, and a few keystrokes each time. Most people, it seems, find it to be a too much effort. 

That describes the original post entirely.